This invention relates to a water supply apparatus for continuously supplying wetting water to the plate on a plate cylinder of a printing press.
In lithographic printing an original (or a mother) printing pattern is formed on the surface of a plate which has been pretreated to be hydrophilic with a transfer or photo plate manufacturing technique, and then the plate is chemically treated to provide a final product, that is, a lithographic printing plate. The plate is mounted on a plate cylinder, and printing ink and wetting water are supplied to the plate at the time of printing. Water is repelled at those portions of the pattern which are oilphilic, whereas water is absorbed by hydrophilic portions so that when oily ink is supplied to the plate, the ink adheres to the oilphilic portions whereas the ink is repelled at other portions, thus forming an ink picture pattern which is transfer printed onto a sheet of printing paper.
The water supply apparatus utilized for this purpose includes a water feed roller rotating in a water container, a swinging roller and a transfer roller supported by a swinging lever to reciprocate between the water feed roller and the swinging roller to intermittently transfer the water on the water feed roller to the swinging roller. The water transferred to the transfer roller is supplied to the plate cylinder.
With this water supply apparatus, since water is supplied intermittently by the reciprocating motion of the transfer roller, water feed becomes nonuniform which results in variations in the quantity of the deposited ink, thus impairing the quality of the printed matter. To obviate this difficulty, various forms of improved water supply apparatus have been proposed which can continuously supply wetting water without using the transfer roller.
FIG. 1 of the accompanying drawings illustrates one known example of such continuous water supply apparatus disclosed in U.S. Pat. No. 3,411,442, in which a plurality of inking rollers 2 are removably mounted on a plate cylinder 1 for continuously and uniformly supplying wetting water to a plate mounted on the plate roller from an ink pot, not shown. The water supply apparatus 3 includes a water feed roller 5 rotating in a water container 4, a transfer roller 6 rotating in the opposite direction with respect to the water feed roller 5, a water quantity adjusting roller 7 in contact with both rollers 5 and 6 and rotating in the same direction as the water feed roller 5, and a water applying or water supply roller 8 removably mounted on the plate cylinder 1. Between one of the inking rollers 2 and the water supply roller 8 is disposed an intermediate roller 9 in contact with the two rollers 2 and 8. At the commencement of the printing operation, the water supply roller 8 is separated away from the plate cylinder 1; the water in the container 4 is admixed with ink on the inking rollers 2 through the water feed roller 5, the adjusting roller 7, the transfer roller 6, water supply roller 8 and the intermediate roller 9; and the mixture of water and ink is then supplied to the plate cylinder 1. After starting the printing operation the water supply roller 8 is brought into contact with the plate cylinder 1 to directly supply water.
With the water supply apparatus 3 thus far described, the ink films on the inking rollers 2 are thick and the water tends to be admixed with ink. Most of the water remains on the inking rollers 2 without being transferred to the plate cylinder 1 so that the quantity of water returned to the water supply roller 8 is extremely small. Further, the water not absorbed by paper after being supplied to the plate cylinder can not return to the water supply roller. Accordingly, the quantity of water supplied by the water supply apparatus must be accurately adjusted which requires a high degree of skill. When the adjusting operation requires a long time, a large quantity of unsatisfactory printed matter is produced meaning a loss of paper. Where a large quantity of water is admixed with ink, the ink is excessively emulsified which greatly impairs the quality of the printed matter. In an extreme case this makes it impossible to print.